#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <utility>
#include <cmath>

#define INF_LL 9000000000000000000
#define INF 2000000000

#define REP(i, n) for(int i = 0;i < (n);i++)
#define FOR(i, a, b) for(int i = (a);i < (b);i++)

using namespace std;

typedef long long ll;
typedef pair<int, int> PII;

class Union_find{
private:
	vector<int> par;
	vector<int> rank;
	int n;

public:
	Union_find(int a){
		n = a;
		for(int i = 0;i < n;i++){
			par.push_back(i);
			rank.push_back(0);
		}
	}

	int find(int x){
		if(par[x] == x){
			return x;
		}else{
			return par[x] = find(par[x]);
		}
	}

	void unite(int x, int y){
		x = find(x);
		y = find(y);
		if(x == y) return;

		if(rank[x] < rank[y]){
			par[x] = y;
		}else{
			par[y] = x;
			if(rank[x] == rank[y]) rank[x]++;
		}
	}

	bool same(int x, int y){
		return find(x) == find(y);
	}
};

int main(void){
	int n, m, x, y;
	cin >> n >> m >> x >> y;

	x--;
	y--;
	int x_c, y_c;
	if(x % (2*m) < m){
		x_c = x % (2*m) + 1;
	}else{
		x_c = 2*m - (x % (2*m)); 
	}

	if(y % (2*m) < m){
		y_c = y % (2*m) + 1;
	}else{
		y_c = 2*m - (y % (2*m)); 
	}

	if(x_c == y_c) cout << "YES" << endl;
	else cout << "NO" << endl;

	return 0;
}